Heat-sensitive recording material

ABSTRACT

A heat-sensitive recording material is described, comprising a support having provided thereon a recording layer comprising a binder containing a diazonium compound and a coupling component, said diazonium compound being a diazonium salt represented by formula (I) 
     
         ArN.sub.2.sup.+ X.sup.-                                    (I) 
    
     wherein Ar represents a substituted or unsubstituted aromatic moiety; and X -  represents an acid anion containing an alkyl group having three or more fluorine atoms.

FIELD OF THE INVENTION

This invention relates to a heat-sensitive recording material, andparticularly to a diazonium heat-sensitive recording material capable ofbeing fixed. Still more particularly, it pertains to a heat-sensitiverecording material which has an excellent storage properties prior tothermal recording, which provides high coloration density upon thermalrecording, and which can be fixed by light after thermal recording.

BACKGROUND OF THE INVENTION

Heat-sensitive recording methods have recently been increasingly used inthe fields of facsimile and printers, due to advantages such as:

(1) no development step is required;

(2) paper quality is approximately that of ordinary paper when paper isused as the support;

(3) handling is easy;

(4) high coloration density is obtained;

(5) recording equipment therefor is simple and inexpensive; and

(6) no noise is produced upon recording.

As heat-sensitive recording materials for such methoods, leucocoloration type heat-sensitive recording materials excellent incoloration density and coloration rate are predominantly used. However,leuco coloration type heat-sensitive recording materials have certaindefects, in that (1) they can form color by handling after recording,(2) by heat, (3) by adhesion of a solvent to stain recording images, and(4) the formed color is removed by plasticizer contained in cellophanetapes.

In order to prevent coloration caused by careless handling, it has beenknown to add a particulate wax as disclosed in Japanese PatentPublication No. 14531/75 or to provide a coating layer for preventingpermeation of the plasticizer as disclosed in Japanese Utility ModelApplication (OPI) No. 125354/81 (the term "OPI" as used herein refers toa "published unexamined Japanese Application"). However, thesetechniques are still unsatisfactory, and, where the possibility offalsification must be avoided, heat-sensitive recording materials havenot been used. Thus, it has been eagerly desired to improve them. As atechnique of preventing coloration in undesired portions after themalrecording, it has been known to use a heat-sensitive recording materialcomprising a diazonium compound, a coupling component, analkali-producing agent, or a coloration aid, and, after thermalrecording, irradiate the material with light to decompose unreacteddiazonium compound for the purpose of stopping further coloration, asdisclosed in Japanese Patent Application (OPI) Nos. 123086/82, 125092/82(corresponding to U.S. Pat. No. 4,411,979), U.S. Pat. No. 3,281,244,etc.

However, this recording material has the defect that it can undergogradual pre-coupling during storage to produce unfavorable coloration(fog). Therefore, at least one of the color-forming components isallowed to exist in the form of non-continuous particles (i.e., a soliddispersion) to prevent the components from contacting with each other,thereby preventing precoupling. However, shelf storage properties ofsuch recording material are still insufficient.

As another technique, it is known to separate the diazonium compound andthe coupling component from each other by incorporating them indifferent layers for minimizing the contact therebetween. This techniqueimproves shelf storage stability, but it concurrently so deterioratesthermal coloration properties that the material based on this techniquefails to respond to high-speed recording with short pulse width.

Further, it is known to encapsulate either a coupling component or analkali component with a non-polar wax substance (Japanese PatentApplication (OPI) Nos. 4414/82 and 142636/82) or with a hydrophobic highmolecular weight substance (Japanese Patent Application No. 192944/82)for separating it from the other component.

This encapsulating technique involves complicated steps of dissolvingthe wax or high molecular substance in a solvent, dissolving ordispersing the color-forming component in the resulting solution, thenevaporating off the solvent to form microcapsules.

These techniques have attempted to overcome the fundamental fact thatdiazonium compounds possess a considerable solubility in water, but, inmany cases, high-speed printability is sacrificed for the sake ofimproving shelf storage properties of heat-sensitive recordingmaterials.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide aheat-sensitive recording material which shows a high coloration speedand a high coloration density, and which has an excellent shelf storageproperties and scarcely undergoes increased fogging under typicaltemperature and humidity conditions.

Another object of the present invention is to provide a heat-sensitiverecording material which enables prevention of coloration in undesiredportions (hereinafter referred to as fixing) by photodecomposingunreacted diazonium compound after thermal recording.

A further object of the present invention is to provide a heat-sensitivematerial with excellent production adaptability.

Still a further object of the present invention is to provide aheat-sensitive recording material which, after decomposition ofdiazonium compound in exposed portions by photorecording, forms avisible image by heating, to thereby form color in unexposed portions.

Still a further object of the present invention is to provide aheat-sensitive recording material which has excellent shelf storageproperties and which can be produced without a complicated step ofencapsulating diazonium compound.

This invention is a heat-sensitive recording material comprising asupport having provided thereon a recording layer comprising a bindingcontaining a diazonium compound and a coupling component, said diazoniumcompound being a diazonium salt represented by formula (I)

    ArN.sup.+.sub.2 X.sup.-                                    (I)

wherein Ar represents a substituted or unsubstituted aromatic moiety;and X⁻ represents an acid anion containing an alkyl group having 3 ormore fluorine atoms.

DETAILED DESCRIPTION OF THE INVENTION

This diazonium compound can maintain its properties and avoid undergoingan increase in fog even in a solid dispersed state.

The diazonium compounds of the present invention are described in moredetail below.

The aromatic moiety represented by Ar is, preferably, represented byformula (II) ##STR1## wherein R₁ represents a hydrogen atom, asubstituted amino group, an alkoxy group having from 1 to 18 carbonatoms, an aryloxy group having from 6 to 18 carbon atoms, an alkylthiogroup having from 1 to 18 carbon atoms, an arylthio group having from 6to 18 carbon atoms, an arylamino group having from 6 to 18 carbon atoms,or an acylamino group having from 1 to 18 carbon atoms; said substitutedamino group preferably including a dialkylamino group having from 1 to36 carbon atoms, an arylamino group having from 6 to 18 carbon atoms, amorpholino group, a piperidino group, a pyrrolidino group, etc., and R₂represents a hydrogen atom, an alkyl group having from 1 to 5 carbonatoms, a halogen atom (e.g., I, Br, Cl, F), an alkoxy group having from1 to 18 carbon atoms, an aryloxy group having from 6 to 18 carbon atoms,or an arylamino group having from 1 to 18 carbon atoms.

Specific examples of the diazonium forming salts are4-diazo-1-dimethylaminobenzene, 4-diazo-1-diethylaminobenzene,4-diazo-1-dipropylaminobenzene, 4-diazo-1-dibenzylaminobenzene,4-diazo-1-dibenzylaminobenzene, 4-diazo-1-ethylhydroxyethylaminobenzene,4-diazo-1-diethylamino-3-methoxybenzene,4-diazo-1-dimethylamino-2-methylbenzene,4-diazo-1-benzylamino-2,5-diethoxybenzene, 4-diazo-1-morpholinobenzene,4-diazo-1-morpholino-2,5-diethoxybenzene,4-diazo-1-morpholino-2,5-dibutoxybenzene, 4-diazo-1-anilinobenzene,4-diazo-1-toluylmercapto-2,5-diethoxybenzene,4-diazo-1,4-methoxybenzoylamino-2,5-diethoxybenzene, etc.

X⁻ represents an acid anion containing an alkyl group having 3 or morefluorine atoms, with the number of fluorine atoms preferably being 9 ormore. The alkyl group includes unsaturated alkyl groups such as alkenylgroups. The number of carbon atoms of the alkyl group is preferably 20or less.

The acid anion represented by X⁻ is preferably represented by formula(III)

    Y--Z--W.sup.-                                              (III)

wherein Y represents a fluorine-containing alkyl group, such that when Yis a saturated fluorine-containing alkyl group, Y is specificallyrepresented by formula (IV)

    C.sub.n H.sub.m F.sub.2n-m+1.sup.-                         (IV)

(wherein n represents an integer of 1 to 18, and m represents an integerof 0 to 2n-2, preferably 9 or more fluorine atoms), and such that when Yis an unsaturated fluorine-containing alkyl group, Y is represented byformula (V)

    C.sub.n H.sub.m F.sub.2n-m-1.sup.-                         (V)

(wherein n represents an integer of 2 to 18, and m represents an integerof 0 to 2n-4, preferably 9 or more fluorine atoms);

Z represents a linkage connecting Y and W⁻ to each other directly orthrough a divalent linking group (as the divalent group, various suchgroups known in the field of organic chemistry can be used and thisinvention is not limited to specific groups; examples include --O--,--S--, --OCH₂ CH₂ --, ##STR2## --SO₂ N(C₂ H₅)C₂ H₄ O--, etc.); and

W⁻ represents an ion moiety such as COO⁻, SO₃ ⁻ or PO₄ ⁻.

Specific examples of diazonium compounds (diazonium salts) according toformula (I) are set forth below. ##STR3##

The coupling component to be used in the present invention is a compoundwhich couples with a diazo compound in a basic environment to form adye. Specific examples thereof include 2-hydroxy-3-naphthoic acidanilide, 1-hydroxy-2-naphthoic acid morpholinopropylamide,2-hydroxy-3-naphthoic acid morpholinopropylamide, 2-hydroxy-3-naphthoicacid-2'-methylanilide, 2-hydroxy-3-naphthoic acid octylamide,2-hydroxy-3-naphthoic acid N-dodecyloxypropylamide,1-phenyl-3-methyl-5-pyrazolone, etc.

In the present invention, it is preferable to incorporate a substancethat becomes a basic compound by heat (basic substance). Examples of thebasic substance include triphenylguanidine, diphenyl-o-tolylguanidine,diphenyl-p-tolylguanidine, 2-benzylimidazole, 4-phenylimidazole,2-phenyl-4-methylimidazole, 2-undecylimidazoline, 4,4'-dithiomorpholine,2-aminobenzothiazole, and 2-benzoylhydrazinobenzothiazole.

These diazonium compound, coupling component, and basic substance may beused in combinations of two or more.

As a stabilizing agent to be used in the present invention, thosesubstances which are used for ordinary diazonium type copying papers maybe used. Specific examples thereof include phosphoric acid, boric acid,tartaric acid, citric acid, salicyclic acid, palmitic acid, thiourea,urea, ammonium salicylate, ammonium carbonate, etc.

As a melting point-reducing agent, known substances may be used.Specific examples thereof include an alcohol derivative, a wax, apolyhydric alcohol ester of higher fatty acid, amides, a metal salt ofhigher fatty acid, a higher straight chain glycol, etc.

The heat-sensitive recording material of the present invention can beobtained in a manner as described in, for example, U.S. Pat. No.4,387,150 . That is, a diazonium compound, a coupling component, and abasic substance are separately, or, if desired, simultaneously milledinto particles of several microns or less in a binder of a suitableconcentration using a mill such as ball mill. Proper amounts of theresulting dispersions were mixed, and a stabilizing acid, anantioxidant, and a melting point-reducing agent are properly addedthereto. Then, the resulting mixture is coated on a support to prepare aheat-sensitive paper capable of being fixed.

As to be preferred amounts to be employed, the coupling component isused in an amount of from 0.1 to 10 parts by weight, and the basicsubstance is used in an amount of from 0.1 to 20 parts by weight, perpart by weight of the diazonium compound. The diazonium compound ispreferably coated so that the amount in the recording layer is from 0.05to 2.0 g/m². The binder is coated preferably such that the amount(solids) in the recording layer is from 0.5 to 5 g/m².

As the binder, polyvinyl alcohol, methyl cellulose, carboxymethylcellulose, hydroxymethyl cellulose, gum arabic, gelatin, casein,styrene-maleic anhydride copolymer, polyacrylamide, etc., can be used.

As the support, paper is generally used, but synthetic resin film,laminated paper, etc., are also usable.

The present invention will now be described in more detail by referenceto examples and comparative examples. However, the invention is notlimited to these examples.

EXAMPLE 1 (1) Preparation of a Solid Dispersion of Diazonium Compound

    ______________________________________                                        5% Polyvinyl Alcohol     100 g                                                Diazonium Salt of the Following Formula:                                                                10 g                                                 ##STR4##                                                                     ______________________________________                                    

The above-described composition was milled in a ball mill for 24 hoursto form a dispersion. The mean particle size was 1.5μ.

(2) Preparation of a Solid Dispersion of Coupling Component

    ______________________________________                                        4% Polyvinyl Alcohol                                                                            100         g                                               Naphthol As       20          g                                               ______________________________________                                    

The above-described composition was milled in a ball mill for 24 hoursto form a dispersion. The mean particle size was 2μ.

(3) Preparation of a Solid Dispersion of Basic Substance

    ______________________________________                                        4% Polyvinyl Alcohol                                                                            100         g                                               Triphenylguanidine                                                                              20          g                                               ______________________________________                                    

The above-described composition was milled for 24 hours in a ball millto form a dispersion. The mean particle size was 2μ.

(4) Preparation of a Coating Solution for Forming a Heat-Sensitive Layer

    ______________________________________                                        Tartaric Acid            0.1     g                                            Ethylthiourea            0.2     g                                            Diazonium Compound Solid Dispersion (1)                                                                2       g                                            Coupling Component Solid Dispersion (2)                                                                4       g                                            Basic Substance Solid Dispersion (3)                                                                   4       g                                            5% Polyvinyl Alcohol     2       g                                            ______________________________________                                    

The above-described composition was coated in a dry amount of 5.5 g/m².

EXAMPLE 2

A heat-sensitive paper was prepared in the same manner as in Example 1except for using, as a diazonium compound in (1) of Example 1, thefollowing diazonium compound: ##STR5##

EXAMPLE 3

A heat-sensitive paper was prepared in the same manner as in Example 1except for using, as a diazonium compound in (1) of Example 1, thefollowing diazonium compound: ##STR6##

COMPARATIVE EXAMPLE 1

A heat-sensitive paper was prepared in the same manner as in Example 1except for using, as a diazonium compound in (1) of Example 1, thefollowing diazonium compound: ##STR7##

COMPARATIVE EXAMPLE 2

A heat-sensitive paper was prepared in the same manner as in Example 1except for using, as a diazonium compound in (1) of Example 1, thefollowing diazonium compound: ##STR8##

The thus-prepared heat-sensitive recording papers were heat-printedusing Mitsubishi Melfas Printer 600 (mode GIII; made by MitsubishiElectric Corp.) and fixed by uniform exposure using Ricoh Hi-Start Model4 (made by Ricoh Company Ltd.). Blue densities of the thus-obtainedrecorded images were measured by means of a Macbeth reflectiondensitometer. The background of each of the fixed samples was heated to150° C. to examine whether it again formed a blue color or not (fixingproperties). Then, for examining shelf storage properties, each samplewas stored for 7 days in dark room under incubating conditions of 30° C.and 75% RH, followed by measuring background density (fog) after theincubation by means of a Macbeth reflection densitometer to check forthe change in fog as compared to before the incubation.

The results thus obtained are tabulated in Table 1.

                  TABLE 1                                                         ______________________________________                                                                  Density                                             Heat-Sensitive                                                                          Fog Density     of                                                  Recording Before    After     Printed                                                                              Fixing                                   Paper     Incubation                                                                              Incubation                                                                              Letter Properties                               ______________________________________                                        Example 1 0.10      0.18      1.21   Good                                     Example 2 0.09      0.16      1.14   Good                                     Example 3 0.09      0.15      1.17   Good                                     Comparative                                                                             0.26      0.73      1.26   Good                                     Example 1                                                                     Comparative                                                                             0.25      0.48      1.25   Good                                     Example 2                                                                     ______________________________________                                    

As is described above, the use of the diazonium compounds of the presentinvention enabled obtained heat-sensitive recording material having goodstorage properties, which attain high coloration density, and which areable to be fixed.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A heat-sensitive recording material comprising asupport having provided thereon a recording layer, wherein saidrecording layer comprises, in admixture: a binder, a diazonium compound,a coupling component and a basic substance, wherein said diazoniumcompound is a diazonium salt represented by formula (I)

    ArN.sub.2.sup.+ X.sup.-                                    (I)

wherein Ar represents a substituted or unsubstituted aromatic moiety;and X⁻ represents an acid anion containing an alkyl group having 4 ormore carbon atoms and three or more fluorine atoms, wherein said acidanion is selected from the group consisting of COO⁻, SO₃ ⁻ and PO₄ ⁻,wherein said diazonium compound is present in the recording layer in anamount from 0.05 to 2.0 g/m², when said binder is present in an amountof from 0.5 to 5 g/m², wherein said coupling component is present in anamount of from 0.1 to 10 parts by weight per part by weight of saiddiazonium compound and, wherein said basic substance is present in anamount of from 0.1 to 20 parts by weight per part by weight of saiddiazonium compound.
 2. A heat-sensitive recording material as in claim1, wherein the aromatic moiety represented by Ar is represented byformula (II) ##STR9## wherein R₁ represents a hydrogen atom, asubstituted amino group, an alkoxy group having from 1 to 18 carbonatoms, an aryloxy group having from 6 to 18 carbon atoms, an alkylthiogroup having from 1 to 18 carbon atoms, an arylthio group having from 6to 18 carbon atoms, an arylamino group having from 6 to 18 carbon atoms,or an acylamino group having from 1 to 18 carbon atoms; said substitutedamino group including a dialkylamino group having from 1 to 36 carbonatoms, an arylamino group having from 6 to 18 carbon atoms, a morpholinogroup, a piperidino group, a pyrrolidino group; and R₂ represents ahydrogen atom, an alkyl group having from 1 to 5 carbon atoms, a halogenatom, an alkoxy group having from 1 to 18 carbon atoms, an aryloxy grouphaving from 6 to 18 carbon atoms, or an arylamino group having from 1 to18 carbon atoms.
 3. A heat-sensitive recording material as in claim 1,wherein X⁻ represents an acid anion containing an alkyl group having 4to 20 carbon atoms.
 4. A heat-sensitive recording material as in claim2, wherein X⁻ represents an acid anion containing an alkyl group having4 to 20 carbon atoms.
 5. A heat-sensitive recording material as in claim1, wherein the acid anion represented by X⁻ is represented by formula(III)

    Y--Z--W.sup.-                                              (III)

wherein Y represents a saturated fluorine-containing alkyl grouprepresented by formula (IV)

    C.sub.n H.sub.m F.sub.2n-m+1.sup.-                         (IV)

wherein n represents an integer of 4 to 18, and m represents an integerof 0 to 2n-2; Z represents a linkage connecting Y and W⁻ to each otherdirectly or through a divalent linking group; and W⁻ represents an anionmoiety.
 6. A heat-sensitive recording material as in claim 2, whereinthe acid anion represented by X⁻ is represented by formula (III)

    Y--Z--W.sup.-                                              (III)

wherein Y representes a saturated fluorine-containing alkyl grouprepresented by formula (IV)

    C.sub.n H.sub.m F.sub.2n-m+1.sup.-                         (IV)

wherein n represents an integer of 4 to 18, and m represents an integerof 0 to 2n-2; Z represents a linkage connecting Y and W⁻ to each otherdirectly or through a divalent linking group; and W⁻ represents an anionmoiety.
 7. A heat-sensitive recording material as in claim 1, whereinthe acid anion represented by X⁻ is represented by formula (III)

    Y--Z--W.sup.-                                              (III)

wherein Y represents an unsaturated fluorine-containing alkyl grouprepresented by formula (V)

    C.sub.n H.sub.m F.sub.2n-m-1.sup.-                         (V)

wherein n represents an integer of 4 to 18, and m represents an integerof 0 to 2n-4; Z represents a linkage connecting Y and W⁻ to each otherdirectly or through a divalent linking group; and W⁻ represents an anionmoiety.
 8. A heat-sensitive recording material as in claim 2, whereinthe acid anion represented by X⁻ is represented by formula (III)

    Y--Z--W.sup.-                                              (III)

wherein Y represents an unsaturated fluorine-containing alkyl grouprepresented by formula (V)

    C.sub.n H.sub.m F.sub.2n-m-1.sup.-                         (V)

wherein n represents an integer of 4 to 18, and m represents an integerof 0 to 2n-4; Z represents a linkage connecting Y and W⁻ to each otherdirectly or through a divalent linking group; and W⁻ represents an anionmoiety.
 9. A heat-sensitive recording material as in claim 5, wherein X⁻has 9 or more fluorine atoms.
 10. A heat-sensitive recording material asin claim 6, wherein X⁻ has 9 or more fluorine atoms.
 11. Aheat-sensitive recording material as in claim 7, wherein X⁻ has 9 ormore fluorine atoms.
 12. A heat-sensitive recording material as in claim8, wherein X⁻ has 9 or more fluorine atoms.
 13. A heat-sensitiverecording material as in claim 1, wherein the coupling component isselected from the group consisting of 2-hydroxy-3-naphthoic acidanilide, 1-hydroxy-2-naphthoic acid morpholinopropylamide,2-hydroxy-3-naphthoic acid morpholinopropylamide, 2-hydroxy-3-naphthoicacid-2'-methylanilide, 2-hydroxy-3-naphthoic acid octylamide,2-hydroxy-3-naphthoic acid N-dodecyloxypropylamide and1-phenyl-3-methyl-5-pyrazolone.
 14. A heat-sensitive recording materialas in claim 1, wherein the binder is selected from the group consistingof polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose,hydroxymethyl cellulose, gum arabic, gelatin, casein, styrene-maleicanhydride copolymer and polyacrylamide.
 15. A heat-sensitive recordingmaterial as in claim 1, wherein the basic substance is selected from thegroup consisting of triphenylguanidine, diphenyl-o-tolylguanidine,diphenyl-p-tolylguanidine, 2-benzylimidazole, 4-phenylimidazole,2-phenyl-4-methylimidazole, 2-undecylimidazoline, 4,4'-dithiomorpholine,2-aminobenzothiazole and 2-benzoylhydrazinobenzothiazole.
 16. Aheat-sensitive recording material as in claim 2, wherein the basicsubstance is selected from the group consisting of triphenylguanidine,diphenyl-o-tolylguanidine, diphenyl-p-tolylguanidine, 2-benzylimidazole,4-phenylimidazole, 2-phenyl-4-methylimidazole, 2-undecylimidazoline,4,4'-dithiomorpholine, 2-aminobenzothiazole and2-benzoylhydrazinobenzothiazole.